Analysis on the thickness and temperature dependent DC breakdown of low density polyethylene

The dc breakdown strength of low density polyethylene (LDPE) decreases with an increase in thickness and temperature of the sample. The breakdown strength is influenced by the charge transport and electric field distortion, and is also related to the molecular chain displacement and fracture. This paper investigates mutual relations among the charge transport, molecular chain displacement, and thickness dependent dc breakdown of LDPE. A model that combines the dynamics of charge transport and molecular displacement is used to calculate the space charge accumulation, molecular chain displacement, and dc breakdown properties of LDPE with various thicknesses at various constant voltage ramping rates. The model includes processes of charge injection, charge migration via hopping between shallow traps, charge trapping at and detrapping from deep traps, charge recombination, and molecular chain displacement. The simulation results show that the breakdown field as a function of sample thickness satisfies an inverse power law for various voltage ramping rates. This is consistent with experimental results. The model can also explain the result that the breakdown field increases with an increase in voltage ramping rate. It also demonstrates the negative correlation between the breakdown field and temperature, which is also in good agreement with experimental results.